1. Field of the Invention
This invention is generally directed to room air purifiers for use in removing smoke, dust, pollen, bacteria and other particulate matter from the air and particularly to portable air purifiers which utilize high efficiency particulate air (HEPA) filters which have an efficiency for removing 99.97% of the particles of a size 0.3 micron or larger from the air in a room. The purifiers are designed to maintain a flow rate of between approximately 150 to 400 cubic feet per minute with the lower rates applying when the filters have become clogged. The purifiers are designed so that the air flow therefrom will pulsate when such flow drops to a lower preselected rate to thereby provide a positive indication that the filters should be replaced. The filters are easily replaceable and may be combined in series or stacked relative to one another in order to increase the overall flow rate through the purifiers.
2. History of the Art
In recent years there has been a growing interest to improve environmental air conditions as the general ambient air has become more polluted. As more information is made available to the public concerning environmental conditions, there has been an increased demand for products which can be used to effectively improve air quality.
As the number of airborne pollutants continues to increase, the effects upon the public have resulted in an increased number of complaints of respiratory infections, burning eyes, allergies, athsma attacks and other symptoms which are directly related to air pollution. One only need to consider the types of airborne particles which are inhaled by the average person on a daily basis to understand that the problem with airborne pollutants is ever increasing and its side effects growing. People are constantly inhaling particles of dust, smoke, pollen, molds, acids, bacteria, carbon and the like. Because of this situation, it has become necessary in many environments, such as in hospitals, laboratories, scientific research rooms and the like, to provide filtering equipment which will remove a majority of these airborne pollutants.
Due to the ever increasing public awareness and the increasing problems resulting from air pollution, a great demand has been made for products which can be made available to the general public to provide for clean air conditions in homes and places of employment. Unfortunately, many of the products which have been advertised, distributed and sold for individual consumers have not been as effective as the equipment used in more commercial environments. There are numerous room air purifiers on the market today which are advertised as being portable and available for consumer use at home, at work or for travel. Many of these units are advertised as being effective to remove substantially all foreign particles from the air; a claim which cannot be supported through actual testing of such devices. Other available portable room air purifiers utilize filtering materials which are only useful for removing perhaps as much as 80-85% of the particles of one micron or larger from the air. Such units therefore do not provide relief against smaller particles such as contained in smoke and dust and also do not provide total relief from larger pollutants such as pollens and fungus spores.
In more recent years, it has been proposed to utilize electrostatic air filtration as a means for providing a more purified air environment. However, tests indicate that electrostatic air purifiers may not remove more than 80% of the particles that pass therethrough. In addition, the efficiency of such units decreases with larger particles and, therefore they do not provide adequate relief against plant pollens. Electrostatic air purification units also produce an ozone byproduct and create charged particles which are attracted to surfaces within a room.
Currently, some manufacturers have begun to make use of high efficiency particulate air filters and some of these manufacturers have made units available for the individual consumer. High efficiency particulate air filters are known as HEPA filters and are defined by federal standard No. 209 B. The general definition for HEPA filters by federal standard is "a filter as specified in MIL-F-51068 with a minimum efficiency of 99.97% as determined by tests". A recent proposal has been made to change the federal standard with regard to HEPA filters to read "a throw-away extended media dry-type filter in a rigid frame having minimum particle-collection efficiency of 99.97% for 0.3 micrometer thermally-generated dioctyl phthalate (DOP) (or specified alternative) aerosol particles, and a maximum clean filter pressure drop of 1.0 inch (2.54 cm) water gauge when tested at rated air flow capacity." The general industry definition of a HEPA filter is one which is efficient in removing 99.97% of the airborne particles of the size of 0.3 microns or larger.
The use of HEPA filters offers an advantage over prior art filter media in that the amount of airborne pollutants which can be effectively removed from the air is significantly increased. In addition, it has been found that HEPA filters last for longer periods of time and therefore offer cost savings to the consumer.
Although some HEPA filter room air purifiers are available for consumer purchase, many of these units do not provide sufficient air flow to be effective for use in a consumer's home and have limited use in very small, closed areas. It is necessary that a room air purifier create an air flow which will insure that all the air within a room is circulated through the filter media as often as possible to insure continuous removal of pollutants. This consideration is even more important when considering that centralized heating and air-conditioning systems continuously circulate contaminated air into the various areas of homes and/or office spaces.
Another consideration which has not been satisfactorily dealt with by prior art room air purifiers is that of informing the consumer when filter elements should be changed. Various prior art filters for other uses have incorporated special valving arrangements to create a whistling noise when the pressure drop through such filters reaches a certain level. In other prior art devices, electronic circuitry is used to sense the number of particles which pass through a filter media with a warning being given if the number of particles exceeds the predetermined number. In other strucures, the air flow rates from the air purifiers are used to determine if the filters should be replaced. The foregoing measures do not adequately rely on the condition of the filter itself to regulate information with regard to the need for filter replacement but rely on either expensive circuity and electronics or valving arrangements to create audible sounds.
Another consideration which has not been appreciated by prior art portable room air purifiers is the need to make such units expansible to provide for varying air flow demand in different areas without requiring separate units of differing capacity to be placed in such areas. Also, many commercially available air purification units are somewhat large and bulky. A large size is often necessary to provide sufficient air filter surface area to adequately remove airborne particles from the air. On the other hand, some air purification units are purposely made smaller to be more portable, however, the volume of air which can be filtered by such units is appreciably reduced and therefore the overall efficiency of such units is decreased.